Neural tube defects (NTDs) are amongst the most common of the major congenital malformations observed in human populations. The incidence of these malformations varies widely in different populations and geographic locales. Recent evidence suggest an elevated rate of NTDs in several different Hispanic populations. Additional recent investigations have reported increased risk of various congenital malformations in association with environmental exposure to pesticides. A case-control study is proposed to evaluate the hypothesis that environmental and/or occupational exposure to specific pesticides are associated with an increase in risk for the development of anencephaly and other birth defects. It will focus on the primarily Hispanic population in south Texas known to have elevated rates of NTDs. One of the counties to be Included (Cameron County) has been the recent targets of a cluster evaluation by the Texas Department of Health and the Centers for Disease Control, which reported a greater than fourfold excess of anencephaly in offspring of mothers who reported they were exposed to aerial, spraying of pesticides. The proposed study will test the following hypotheses: 1) that environmental exposure to specific pesticides may increase the risk of anencephaly; 2) that environmental exposure to specific pesticides may Increase the risk of spina bifida, esophageal atresia, anorectal atresia, renal agenesis/dysgenesis, arthrogryposis, and limb reduction defects; 3) that deficiency in dietary levels of folic acid increased the risk of NTDs in the study populations. Detailed information on medical, occupational and dietary history will be obtained by in-person interview of subject mothers in either Spanish or English. Dietary folate will be assessed by a 24 hour recall questionnaire. Environmental exposure will be evaluated by testing water and soil samples by immunoassay, GC/MS, and HPLC for specific pesticides.